The excitatory amino acid L-glutamate (at times referred to herein simply as glutamate) through its many receptors mediates most of the excitatory neurotransmission within the mammalian central nervous system (CNS) and has been implicated in numerous peripheral nervous system (PNS) pathways. The excitatory amino acids, including glutamate, are of great physiological importance, playing a role in a variety of neurological, physiological and psychiatric processes, such as synaptic plasticity, motor control, respiration, cardiovascular regulation, sensory perception, and emotional responses.
Glutamate acts via at least two distinct classes of receptors. One class is composed of the ionotropic glutamate (iGlu) receptors that act as ligand-gated ion channels. Via activation of the iGlu receptors, glutamate is thought to regulate fast neuronal transmission within the synapse of two connecting neurons in the CNS. The second general type of receptor is the G-protein or second messenger-linked “metabotropic” glutamate (mGlu) receptor. Both types of receptors appear not only to mediate normal synaptic transmission along excitatory pathways, but also participate in the modification of synaptic connections during development and throughout life. Schoepp, Bockaert, and Sladeczek, Trends in Pharmacol. Sci., 11, 508 (1990); McDonald and Johnson, Brain Research Reviews, 15, 41 (1990).
The mGlu receptors belong to the Class C G-protein coupled receptor (GPCR) family. This family of GPCR's, including the calcium-sensing receptors, GABAB receptors and sensory receptors, are unique in that effectors bind to the amino-terminus portion of the receptor protein translating a signal via the transmembrane segments to the intracellular matrix through receptor/G-protein interactions. Ozawa, Kamiya and Tsuzuski, Prog. Neurobio., 54, 581 (1998). It has been demonstrated that the receptors are localized either pre- and/or post-synapticly where they can regulate neurotransmitter release, either glutamate or other neurotransmitters, or modulate the post-synaptic response of neurotransmitters, respectively.
At present, there are eight mGlu receptors that have been positively identified, cloned, and their sequences reported. These are further subdivided based on their amino acid sequence homology, their ability to effect certain signal transduction mechanisms, and their known pharmacological properties. Ozawa, Kamiya and Tsuzuski, Prog. Neurobio., 54, 581 (1998). For instance, the Group I mGlu receptors, which include the mGlu1 and mGlu5, are known to activate phospholipase C(PLC) via Gαq-proteins thereby resulting in the increased hydrolysis of phosphoinositides and intracellular calcium mobilization. There are several compounds that are reported to activate the Group I mGlu receptors including DHPG, (+/−)-3,5-dihydroxyphenylglycine. Schoepp, Goldworthy, Johnson, Salhoff and Baker, J. Neurochem., 63, 769 (1994); Ito, et al., Neurorep., 3, 1013 (1992). The Group II mGlu receptors consist of the two distinct receptors, mGlu2 and mGlu3 receptors. Both receptors are negatively coupled to adenylate cyclase via activation of Gαi-protein. These receptors can be activated by a group-selective compound such as (1S,2S,5R,6S)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate. Monn, et al., J. Med. Chem., 40, 528 (1997); Schoepp, et al., Neuropharmacol., 36, 1 (1997). Similarly, the Group III mGlu receptors, including mGlu4, mGlu6, mGlu7 and mGlu8, are negatively coupled to adenylate cyclase via Gαi and are potently activated by L-AP4 (L-(+)-2-amino-4-phosphonobutyric acid). Schoepp, Neurochem. Int., 24, 439 (1994).
It should be noted that many of the available pharmacological tools are not ideal in that they cross react not only on the receptors within a group of mGlu receptors but also often have some activity between groups of mGlu receptors. For instance, compounds such as 1S,3R-ACPD, (1S,3R)-1-aminocyclopentane-trans-1,3-dicarboxylic acid, are believed to activate all of the Group I, II and III mGlu receptors depending upon the dose utilized while others, such as 1S,3S-ACPD, (1S,3S)-1-aminocyclopentane-trans-1,3-dicarboxylic acid, are more selective for the Group II receptors (mGlu2/3) than the Group I (mGlu1/5) or Group III (mGlu4/6/718). Schoepp, Neurochem. Int., 24, 439 (1994). To date, there are very few examples of selective agents for the mGlu receptors. Schoepp, Jane, and Monn, Neuropharmacol., 38, 1431 (1999).
It has become increasingly clear that there is a link between modulation of excitatory amino acid receptors, including the glutamatergic system, through changes in glutamate release or alteration in postsynaptic receptor activation, and a variety of neurological, psychiatric and neuroinflammatory disorders. e.g. Monaghan, Bridges and Cotman, Ann. Rev. Pharmacol. Toxicol., 29, 365-402 (1989); Schoepp and Sacann, Neurobio. Aging, 15, 261-263 (1994); Meldrum and Garthwaite, Tr. Pharmacol. Sci., 11, 379-387 (1990). The medical consequences of such glutamate dysfunction make the abatement of these neurological processes an important therapeutic goal.
Leukotrienes are potent local mediators, playing a major role in inflammatory and allergic responses including arthritis, asthma, psoriasis, and thrombotic disease. Leukotrienes are straight chain eicosanoids produced by the oxidation of arachidonic acid by lipoxygenases in several cell types including: eosinophils, neutrophils, mast cells, leukocytes, and macrophages. At the present time, there are two established Class A GPCR receptors for the cysteinyl-leukotrienes (CysLT1 and CysLT2) which the leukotrienes LTC4, LTD4 and LTE4 activate, mediating their proinflammatory effects. Each of the CysLT receptors has distinct tissue distributions and associations with physiological responses. Also, the leukotriene LTD4 has a higher affinity for the CysLT1 receptor than the other leukotrienes. Back, M. Life Sciences 71, 611-622, (2002). The leukotrienes, especially LTD4 and its receptor CysLT1, have been implicated in the pathogenesis of airway and allergic diseases such as asthma by contributing to bronchoconstriction, mucus secretion, and eosinophil migration. Thus, leukotrienes have been shown to play an important role in the pathology of asthma. Rigorous proof for the role of leukotrienes in asthma has been provided by several pivotal clinical trials in which orally administered LTD4 receptor antagonists produce clear therapeutic benefit in asthma patients. These benefits include reduction in the use of classic asthma therapies such as corticosteroids. Kemp, J. P., Amer. J. Resp. Medi. 2, 139-156, (2003).
Numerous investigations confirm the importance of the leukotrienes in allergic disorders as well. Thus, after allergen provocation, a marked increase in the LT concentration in the nasal lavage fluid of patients with allergic rhinitis was detected both in the early phase and in the late phase. Creticos, P. S., S. P. Peters, N. F. Adkinson, R. M. Naclerio, E. C. Hayes, P. S, Norman, L. M. Lichtenstein, N. Eng. J. Med. 310:1626 (1984). In addition, treatment with clinically efficacious antihistamines, such as azelastine, has shown a reduction in the formation of the cysteinyl-leukotrines, establishing a correlative relationship of allergic reaction symptoms to the degree of leukotriene formation and, thus, CysLT receptor activation. Achterrath-Tuckermann, U., Th. Simmet, W. Luck, I. Szelenyi, B. A. Peskar, Agents and Actions 24:217, 1988; Shin, M. H., F. M. Baroody, D. Proud, A. Kagey-Sobotka, L. M. Lichtenstein, M. Naclerio, Clin. Exp. Allergy 22:289, 1992.
U.S. Pat. No. 6,194,432 B1 discloses a method for using leukotriene antagonist drugs to prevent and treat recurrent primary headaches including migraine headaches.
U.S. Pat. No. 5,977,177 discloses certain substituted phenyl derivative compounds are modulators of endothelin and, as such, are useful in treating many different conditions including asthma.
U.S. Pat. No. 4,853,398 discloses certain benzene derivative compounds are selective antagonists of leukotrienes and, as such, are useful in treating allergic disorders such as asthma.
European Patent Application No. EP 28063 A1 and UK Patent Application No. GB 2058785 disclose certain phenol derivative compounds are antagonists of slow reacting substance of anaphylaxis and, as such, are useful in treating asthma, hay fever and skin afflictions.
Brown, F. J. et al J. Med. Chem. 32, p. 807-826 (1989) discloses certain hydroxyacetophenone derivative compounds are antagonists of leukotrienes and, as such, play a role in treating asthma.
International Patent Application Publication No. WO 2001056990 A2 and U.S. Pat. No. 6,800,651 B2 disclose certain pyridine derivative compounds are potentiators of metabotropic glutamate receptor function, specifically; potentiators of mGlu2 receptor function and, as such, are useful in the treatment of many different conditions including anxiety and migraine headache.
International Patent Application Publication No. WO 2004018386 and Pinkerton, A. B. et al Bioorg. Med. Chem. Lett., 14, p. 5329-5332 (2004) disclose certain acetophenone derivative compounds are potentiators of glutamate receptor function, specifically; potentiators of mGlu2 receptor function and, as such, are useful in the treatment of many different conditions including anxiety, schizophrenia and migraine headache.
Recently, Pinkerton, A. B. et al Bioorg. Med. Chem. Lett., 14, p. 5867-5872 (2004) disclose certain 4-thiopyridyl acetophenone derivative compounds are potentiators of glutamate receptor function, specifically; potentiators of mGlu2 receptor function and, as such, may be useful in the treatment of CNS disorders including anxiety, schizophrenia and epilepsy.
The present invention provides compounds of formula I that are potentiators of the mGlu2 receptor and antagonists of the CysLT1 receptor. As such, compounds of formula I would provide a means to treat disorders associated with glutamate or leukotrienes. In addition, it is anticipated that in disorders with a glutamate and leukotriene component to the onset, propagation and/or symptoms, the compounds of formula I will provide an effective treatment for the patient. The medical consequences of such glutamate dysfunction make the abatement of these neurological processes an important therapeutic goal.